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Plastic is cheaper in quantity, but there's another reason too. You can make plastic parts in shapes and complexities that just aren't practical for metal.

Nonetheless, it seems a bit counterintuitive to make something that is required to withstand high pressures for years out of plastic. I think the fact that mishimoto managed to make an aluminum radiator/expansion tank combination is proof that there were alternative options

Nonetheless, it seems a bit counterintuitive to make something that is required to withstand high pressures for years out of plastic. I think the fact that mishimoto managed to make an aluminum radiator/expansion tank combination is proof that there were alternative options

It is not that plastic is a bad material. It is that the plastic they chose turned out to be a bad material. Plastics/composites can be incredibly strong and durable. Anyway, the problem with the pump is the bearing anyway, isn't it? I don't hear much of the impeller disintegrating.

Nonetheless, it seems a bit counterintuitive to make something that is required to withstand high pressures for years out of plastic. I think the fact that mishimoto managed to make an aluminum radiator/expansion tank combination is proof that there were alternative options

Intuition is one thing. A meaningful comparison of material properties and material performance is what's really needed to determine the best material for the job.

So first, I read that the M3 doesn't have the same set up as non-Ms but I'm not so sure about that. I know there's a hose crossing over to the ET that we don't have, but I think that's just the way it makes the same connection we have to the ET from the upper hose. Just a hose instead of it being incorporated into upper hose fitting.

My car's second ET lasted 9 years. 9 years...and probably a good 200K miles. The first ET was replaced after 2 years.

I do think ET's fail because of overfilling...and made a thread about that...forget the title...maybe 'plastic or human error'?

My window regulator on driver's door was original up until a year or two ago. They're not crappy parts...they're just susceptible to owners who are misinformed, ignorant, dirty, or busy! I think regulators probably fail more because of owners opening windows when they're frozen...or maybe had been closed a long time in the heat and got stuck. Combine that with lack of a preventive and sensual coating of gummi pflege...what do you expect?

Most cars don't have an ET like we do. Jaguar does I know...not sure who else, but not everyone at all.

Our expansion tank is a thermal expansion tank...like in your home's thermal expansion tank. In conventional systems, the extra fluid leaves to overflow tank and returns...as explained. In ours, the air in ET (maybe 2 cups of it) is what buffers, cushions, the system. Air compresses much easier than water, you know, but when coolant heats, it expands and needs a place to go. Don't give it the air, it will take out an ET.

Also, have to say it doesn't bother me having a system that will blow apart before the engine does. If it was as rock solid as it seems some of you want, you'd then be moving extra pressure to where? The head gasket. No thanks, I'd prefer just replacing ET please.

Don't go hating on BMW guys. Continue on like this and your penance will be severe!

__________________

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My window regulator on driver's door was original up until a year or two ago. They're not crappy parts...they're just susceptible to owners who are misinformed, ignorant, dirty, or busy! I think regulators probably fail more because of owners opening windows when they're frozen...or maybe had been closed a long time in the heat and got stuck. Combine that with lack of a preventive and sensual coating of gummi pflege...what do you expect?

Pretty much every BMW since the mid 90s or so has been plagued with window regulator issues. To suggest that parts fail because they needed lubrication (jokingly or otherwise) pretty much confirms they are poorly-designed and/or poorly-made.

Quote:

...the air in ET (maybe 2 cups of it) is what buffers, cushions, the system. Air compresses much easier than water, you know, but when coolant heats, it expands and needs a place to go. Don't give it the air, it will take out an ET.

...no. PV=nRT so temperature and pressure are directly proportional. And pressure is pressure, with or without the air in the system.

If you look at window regulators from German cars made in the 70s and early 80s, they're pretty indestructable. They'll last for decades before a motor or switch will usually fail first. As Icoleman said, the bean-counters have won and we're stuck with the current, cheaper design.

I've owned several older German cars (I keep them a long time) and have yet to experince a regulator failure until my E46 (two failures).

So first, I read that the M3 doesn't have the same set up as non-Ms but I'm not so sure about that. I know there's a hose crossing over to the ET that we don't have, but I think that's just the way it makes the same connection we have to the ET from the upper hose. Just a hose instead of it being incorporated into upper hose fitting.

My car's second ET lasted 9 years. 9 years...and probably a good 200K miles. The first ET was replaced after 2 years.

I do think ET's fail because of overfilling...and made a thread about that...forget the title...maybe 'plastic or human error'?

My window regulator on driver's door was original up until a year or two ago. They're not crappy parts...they're just susceptible to owners who are misinformed, ignorant, dirty, or busy! I think regulators probably fail more because of owners opening windows when they're frozen...or maybe had been closed a long time in the heat and got stuck. Combine that with lack of a preventive and sensual coating of gummi pflege...what do you expect?

Most cars don't have an ET like we do. Jaguar does I know...not sure who else, but not everyone at all.

Our expansion tank is a thermal expansion tank...like in your home's thermal expansion tank. In conventional systems, the extra fluid leaves to overflow tank and returns...as explained. In ours, the air in ET (maybe 2 cups of it) is what buffers, cushions, the system. Air compresses much easier than water, you know, but when coolant heats, it expands and needs a place to go. Don't give it the air, it will take out an ET.

Also, have to say it doesn't bother me having a system that will blow apart before the engine does. If it was as rock solid as it seems some of you want, you'd then be moving extra pressure to where? The head gasket. No thanks, I'd prefer just replacing ET please.

Don't go hating on BMW guys. Continue on like this and your penance will be severe!

M3's ET/Reservoir has a fluid relief - if the coolant level is too high, it will simply get dumped out. Much lower chance of over pressurizing the system. In a non-M, if you overfill, then you very well can cause the average pressures to increase more than the system was designed for.

Btw the change in density of the coolant with temperature will be pretty small. Not enough to create a major effect on pressures. I'm sure it's something the engineers take into account when designing the system, but it's a tiny effect nonetheless.

Quote:

Originally Posted by LeMansteve

Intuition is one thing. A meaningful comparison of material properties and material performance is what's really needed to determine the best material for the job.

I think the trend of E46 expansion tanks failing so frequently compared to the reservoirs of other manufacturers' systems is pretty telling on which material has properties better suited for the job at hand.

Quote:

Originally Posted by lcoleman

...no. PV=nRT so temperature and pressure are directly proportional. And pressure is pressure, with or without the air in the system.

Pressure and temperature are only directly proportional if volume (and # of gas molecules) is constant. Since Dmax is talking about the coolant expanding and taking more volume, the pressure will increase at a non-linear rate (it can be calculated if you know how the density of the coolant changes with temperature).

And Dmax is correct in that the air space acts as a buffer. The less the air volume is, the larger the effect of a fractional volume change on pressure.

My theory has been that the reason why they use plastic is because 1) its cheaper to make I bet and 2) they need parts on these cars to only survive the warrenty period. what happens when the warrenty is over for the second or third owner? they pay right out of pocket. i believe thats why some things on these cars have been designed the way they are

Find me a car out there that does not use plastics in 90% of their cooling system. I have posted extensively about why plastics are NOT a cheaper solution for car makers, and why they like to use them anyway, but I will just give you the broad view:
- The capital costs for plastic molds are HUGE. The one for the thermostat housing would easily be a $750k mold. And you can't just have one. They probably have a dozen. And when they stop making e46 thermostat housings, that mold is just scrap steel, because the only thing it can do is make e46 thermostat housings. Not to mention, the molds wear out. There is a limited number of parts that can be made before it is too worn to produce the dimensionally correct part. Plastic is abrasive to the mold. That single part has probably cost BMW millions of dollars in molds alone.

So, why use them?
- The parts come out of the mold ready to use, for the most part. No machining, no plating, painting, anodizing or other finish required. The same part made from aluminum is labor intensive. It requires casting, then machining operations, then finishing operations. Each of these steps introduces the chance for human error, scrapped parts loss, and dimensional variances, not to mention transportation from one facility to another. But, a part made in a properly operated plastic mold will have almost zero scrap loss, and will come out of the mold complete, and dimensionally correct, each one the same as the other. There is almost no dimensional variance.

Now, you are correct in stating that they will not last like metal parts, but they will outlive the warranty period. And yes, that is all they care about. But this has added a new type of preventative maintenance to cars, because you now have to replace parts based on age, and not because of a failure. It is now just a fact of life that this is the way things will be from now on. It sucks, but it will not stop. In fact, it will expand to other parts as time goes by.

The biggest problem with the ET is that it is very complex, with internal components that mean it has to be hand assembled and bonded together. The failures are mostly due to failures in that bonding process, and the fact that early ET's did not have enough internal bracing in critical areas. I am sure that if they could do it over, they would. It is just too complex, and it relied too much on the integrity of that bonding agent. Even if they had made the pieces with an interlocking joint that was then bonded, it would have been better. Instead, they are bonding two flat surfaces, which is never ideal. I have a feeling that some vendor overstated the ability of their glue to hold these things together through thousands of heating and cooling cycles.
I have not looked at the tanks on the newer models, but I would hope that they have applied some lessons learned from the e46.

Nonetheless, it seems a bit counterintuitive to make something that is required to withstand high pressures for years out of plastic. I think the fact that mishimoto managed to make an aluminum radiator/expansion tank combination is proof that there were alternative options

Unfortunately, we were at the tip of the spear in the drive to design a sealed plastic tank. Every car ends up with one part that is its weak spot, it's Achiles heel. The ET will be that part for our car.
The problem with this thing is that it is so devilishly complicated inside. The fact that they had to assemble parts inside of there should have pushed towards an aliminum canister, but there was probably a management directive that it be made out of plastic. See my other post where I mention a sealant vendor that oversold their products capabilities. If they worked their way into upper management, possibly eating the labor costs themselves to get the chance to use their bonding process, then engineering may have had no chance.